Stator assembly for an axial compressor

Abstract

A device for attaching the stator vanes of an axial compressor to an external housing is disclosed. The attachment utilizes an inner casing, having the vanes mounted on it, and an outer casing surrounding the inner casing in such a manner that differential thermal expansion between the various elements is minimized. This allows more accurate control of the clearances between the rotor and the stator.

We claim: 
     
       1. A stator assembly for an axial compressor to control the relative thermal expansion between the stator assembly and a rotor having a plurality of rotor blades thereon, wherein the stator assembly is disposed about the rotor assembly and comprises: (a) an annular inner casing having an interior surface and an exterior surface, the interior surface defining a plurality of circumferential grooves, the inner casing comprising a plurality of arcuate segments, each segment having parallel lateral edges disposed obliquely to a longitudinal axis of the compressor;   (b) means to attach a plurality of stator vanes to alternate ones of the circumferential grooves in the inner casing;   (c) a plurality of first friction bands;   (d) means to attach the first friction bands in the circumferential grooves between the stator vanes;   (e) an outer casing disposed about the inner casing so as to define an annular space therebetween;   (f) means to direct a portion of the air passing through the compressor into the annular space between the inner and outer casings;   (g) a plurality of first brackets attached to the exterior surface of each arcuate segment of the inner casing, each of the first brackets defining an opening therethrough with its axis extending generally parallel to the longitudinal axis of the compressor, at least one bracket on each arcuate segment being longitudinally aligned with a bracket on an adjacent arcuate segment;   (h) a plurality of second brackets distributed about an interior surface of the outer casing, each of the second brackets defining an opening therethrough, the openings defined by the second brackets being adjacent and aligned with corresponding openings defined by the first brackets; and,   (i) pin means inserted through the aligned openings of the first and second brackets to retain the inner and outer casings in assembled relationship and to attach adjacent arcuate segments together.   
     
     
       2. The stator assembly of claim 1 wherein alternate ones of the circumferential grooves in the interior surface of the inner casing having a generally "U" shaped cross-section, each of the sides of the "U" further defining a recess and wherein the means to attach the plurality of stator vanes comprises: a plurality of segments forming an annular member, the segments being attached to a first end of each of the stator vanes; longitudinal tongues extending from either side of the segments, the tongue shaped so as to be received in the recesses of the circumferential grooves; and, a plurality of "U" shaped rings engaging the sides of alternate ones of the circumferential grooves and extending in a longitudinal direction so as to retain the longitudinal tongues in their respective recesses. 
     
     
       3. The stator assembly of claim 2 further comprising a second plurality of segments attached to a second end of the stator blades, and a second friction band attached to the second segments. 
     
     
       4. The stator assembly of claim 2 wherein the means to attach the first friction bands to the circumferential grooves in the inner casing comprises: a cylindrical element attached to the first friction bands and to a pair of the "U" shaped rings attached to the cylindrical element. 
     
     
       5. The stator assembly of claim 1 further comprising means to lock the pins in their inserted position. 
     
     
       6. The stator assembly of claim 5 wherein the means to lock the pins in their inserted position comprises sealing elements attached between the inner and outer casings to render the annular space between them air tight. 
     
     
       7. The stator assembly of claim 1 further comprising a layer of thermal insulation attached to the interior surface of the outer casing. 
     
     
       8. The stator assembly of claim 1 wherein the outer casing comprises: (a) an upstream section; (b) an intermediate section defining an air intake; and (c) a downstream section. 
     
     
       9. The stator assembly of claim 8 wherein the inner casing comprises an upstream section and a downstream section, the sections being longitudinally spaced from each other to define an air pickup zone to allow a portion of the air passing through the compressor to flow into the annular space between the inner and outer casings.